Light emitting diodes (LEDs) are currently one of the most innovative and fastest growing technologies in the semiconductor industry. While LEDs have been in use for decades as indicators and for signaling purposes, technology developments and improvements have allowed for a broader use of LEDs in illumination applications.
Semiconductors that contain nitrogen (N) as the Group V element have proven to be useful for short-wavelength light emitting devices. Among these, extensive research has been conducted on gallium-nitride based semiconductors for use as light emitting diodes, such as InxGal-xN and AlxGayInzN, and such light emitting diodes (LEDs) have already been put to practical use.
Generally, vertical GaN-based LEDs are grown on a sapphire substrate. The sapphire substrate is rigid and electrically nonconductive and has a low thermal conductivity. In a typical process for making a GaN-based LEDs, a plurality of GaN layers are grown on the sapphire substrate. One or more p-electrodes may then be formed on a p-type GaN layer, and the sapphire substrate is removed using a laser lift off (LLO) process, exposing the n-type layers for subsequent processes.
LLO is one technology used to remove sapphire. However, LLO introduces damage by laser-induced shock waves and can affect yield and result in problems in the device performance and reliability. The sapphire also can be removed by mechanical methods, including grinding, lapping and mechanical chemical polishing (CMP), but the difficulty in planar mounting and uniform polishing within several microns make it difficult to use of this mechanical method and achieve reliable device performance and high yield.
Flip-chip LEDs, one common alternative to vertical LEDs, have a more mature process, but the structure has less thermal dissipation ability due to the air gaps between the device and the heat sink. The mounting and packaging is also expensive when compared to vertical LEDs.
Accordingly, there is a need for a quasi-vertical light emitting diode that addresses these and other shortcomings of known light emitting devices and can achieve the desired performance requirements while reducing the technical challenges and achieving high yield.